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Squeeze casting is a method of forming metal into shapes by using two dies that are squeezed together. Most casting techniques use two dies that are squeezed together before the metal is added but, in squeeze casting, the two are pushed together after the metal is added. This is done with liquid metal, and the upper die is only removed when the metal has cooled. By using this technique, the metal will typically come out stronger, with a better grain and less metallic shrinking. This commonly is done with magnesium, aluminum and their alloys, but many other metals can be used.
Most casting techniques involve the use of two dies, but squeeze casting uses the dies in a different way. The two casts normally are placed together and liquid metal is poured into the case. With a squeeze cast, a pool of liquid metal is placed in the bottom die and an upper die comes in and squeezes the metal into a shape. Pressure is being applied via the upper die, so this is not strictly casting, as it adds forging to create a hybrid technique.
Only liquid metal can be used in this application. While materials such as plastic can melt at high temperatures, this technique will not be suitable to cast plastic. After the upper die is set, workers wait until the metal is completely cool. Once cool, the upper die will be released and the required shape will have been cast into the now-solid metal.
There are several advantages to squeeze casting that increase the metal’s functionality. One benefit is that the metal will typically be stronger, because the cooling method forms a better grain when compared to other casting techniques. There is a tight seal and pressure between the two dies, so less metal is able to evaporate, leading to less shrinking during the cooling process.
Magnesium, aluminum and metals alloyed with these two sources usually are used in squeeze casting, because they are easy to melt and have varied uses. At the same time, nearly any metal can be used in this process. Unless the metal is liquid at room temperature — like mercury — or dangerously radioactive — like plutonium — most low- to medium-temperature melting metals can be used. High-temperature melting metals are often unusable, because they would end up melting the dies or are too difficult to cast correctly without warping or other errors.